The invention relates to an optical transducer element for converting displacements of an object connected to said element into an optical signal, which element comprises a flat body provided with a plurality of dark first strips which in the direction of displacement of the element alternate with bright second strips. The invention also relates to a device for measuring rectilinear or angular displacements of an object provided with such an element.
The term "displacements" is to be interpreted in its widest sense. It is to be understood to mean both linear displacements of an object and rotations of an object about a specific object axis. Since the position of an object is the displacement of this object relative to a reference point and the velocity with which an object moves is the derivative of the displacement with respect to time, the transducer element can also be utilized for determining the position or the velocity of an object.
European Patent Application No. 0,096,448 to which U.S. Pat. No. 4,577,101 corresponds describes a device for determining angular displacements of an object, the transducer element being a transparent disc provided with radially extending radiation-reflecting strips. This disc is arranged between a radiation source and a radiation-sensitive detection system. This system comprises a large number of detectors arranged in line. The displacement of an object, for example a part of a machine tool, or the movement of a manipulator in an automated production machine or measuring apparatus can be measured by imaging the strip pattern of the transducer element onto the corresponding strip pattern of the detection system. The individual detectors of this system supply electric pulses depending on the displacement or the position of the object relative to the detection system, which pulses can be processed electronically to form a measurement signal.
In order to obtain the desired resolution of, for example, 0.005.degree. and the desired reproducibility of, for example, 0.001.degree. of the measuring device the transducer element must comply with very stringent requirements with respect to the width of the strips, i.e. their dimension transverse to the direction of movement and the position of these strips. In a specific version of a currently used transducer element for measuring angular displacements in a goniometer the width of the strips is approximately 318 .mu.m, the positional accuracy of the strip being of the order of 1 .mu.m. The strips comprise, for example, chromium strips on a glass disc. This disc-shaped transducer element, also referred to as "angular position encoder", must be manufactured with special equipment employing known lithography techniques as used in the fabrication of integrated circuits. The known angular-position encoder discs are comparatively expensive.
There is an increasing need for transducer elements for measuring angular displacements as well as rectilinear displacements, which are substantially cheaper and, preferably, also more accurate.